Polymers find uses in a variety of plastic articles including films, sheets, fibers, foams, molded articles, adhesives and many other specialty products. The majority of this plastic material ends up in the solid waste stream. While some efforts at recycling have been made, repeated processing of even pure polymers results in degradation of material and consequently poor mechanical properties. Different grades of chemically similar plastics mixed upon collection can cause processing problems that make the reclaimed material inferior or unusable.
Agricultural items such as erosion control covers, mulches, nets, twines, pots and plant stakes may be formed from plastics. It would be advantageous for such items to be biodegradable. For example, agricultural mulches are used to retard weed growth, increase moisture retention by the soil, and prevent erosion. However, if the mulches are not degradable, the mulch must be removed from the field at the end of each season. It would be efficient to use a mulch which is biodegradable, and did not require removal at the end of the growing season.
Clendinning et al., U.S. Pat. No. 3,932,319, disclose films and containers, which may be used as transplanter containers, fabricated from material comprising a biodegradable thermoplastic dialkanoyl polymer. Clendinning et al. teach that containers may be formed from a blend of the biodegradable thermoplastic dialkanoyl polymer and a naturally occurring biodegradable product such as soya bean meal, peat moss, corn starch, wood chips, flours and starches.
Lahalih et al., U.S. Pat. No. 4,686,790, disclose agricultural mulch films prepared by mixing conventional plant nutrients with a water-soluble polymer, such as polyvinyl alcohol, to form a thin film. Lahalih et al. further teach the dry film is then coated with a thin layer of water-resistant resin, such as polyvinyl acetate, to form a composite mulch film.
Billings, U.S. Pat. No. 5,165,351, discloses a seed planter unit which utilizes a biodegradable seed tape. Billings further teaches that fertilizer and agricultural chemicals may be incorporated into the seed tape or into a separately dispensed tape for controlled application of the chemicals adjacent to the crops.
Aslam et al., U.S. Pat. No. 5,207,020, disclose an erosion control blanket made of recycled, biodegradable, split and expanded sheets of paper. Aslam et al. teach the blanket has a plurality of layers such as the upper layers promote run-off to reduce erosion, while lower layers trap water which passes through the blanket passing the water to the soil and trapping loose soil particles.
Kell, Jr. et al., U.S. Pat. No. 5,503,883, disclose a biodegradable wreath ring comprising a ring constructed from multiple layers of paper strips laminated one over another in the radial direction of the ring and bonded with a biodegradable resin or adhesive.
Sinclair et al., U.S. Pat. No. 5,760,118, disclose that hydrolytically degradable polymers may be used in the production of products for the controlled release of chemicals, such as biocides, fertilizers, attractants to attract pests into traps, repellants, mildewcides, fungicides, and fertilizers. Sinclair et al. further disclose the hydrolytically degradable polymers may be used for garden products such as root ball covers, geo-textile erosion control, weed control film, mulch, seed mats, seed strips, pots, stakes and twines, as well as items such as toys, clothes, absorbent items and containers.
Behel, Jr. et al., U.S. Pat. No. 5,837,029, teach the inclusion of organic hydroxy acids and iron sulfate formulations in hydrophilic polymer delivery systems. Behel, Jr. et al. teach a delivery system forms particles which can be metered into soil in or near a plant row.
Shasha et al., U.S. Pat. No. 5,837,273, teach compositions for encapsulating biologically active material into starch-based adherent granules. Shasha et al. teach such granules are capable of sustained release of pest control agents.
Wood et al., U.S. Pat. No. 5,883,104, disclose methods of improving the residual control of mites and prolonging the protection of plants from mite infestations by applying to plant foliage an unsymmetrical 4,6-bis(aryloxy)pyrimidine compound.
Ballinger, Jr., U.S. Pat. No. 5,885,604, discloses methods for deterring birds from damaging planted seeds by applying to the seeds before planting or to the surface of the ground overlaying the planted seeds a non-toxic solid coating material which is repellant to the taste to birds and absorbs light at a wave length in the range of 300 to 400 mm.
Kim et al., EP 0843963A1, disclose a pesticide formulation comprising pesticide and biodegradable thermoplastic polyester resin. Kim et al. teach the formulation provides for controlled release of the active ingredient.
Asrar et al., WO 99/04948, disclose methods of producing coated objects comprising melting a polyhydroxyalkanote, such as polyhydroxybutyrate or polyhydroxy-butyrate-co-valerate, and extrusion coating the object. Asrar et al. teach the coating has a molecular weight of greater than 125,000 daltons.
Thus, there is continuing need in the agricultural field for items formed from biodegradable plastics. Preferably the plastics would have great flexibility and strength without excessive thickness. Further, it is desirable that such biodegradable plastics be substantially free of or free of plasticizers which may leak from the plastic articles. There is a further need for methods of delaying or controlling the release of agricultural chemicals.
Unfortunately, many biodegradable items are brittle, or are incapable of degrading under both aerobic and anaerobic conditions. Further, prior art polymers such as polyhydroxybutyrate and poly(hydroxybutyrate-co-hydroxyvalerate) often have unsatisfactory properties. Polyhydroxybutyrate and poly(hydroxybutyrate-co-hydroxyvalerate) tend to become thermally unstable near their melt temperatures, which make processing difficult. It is preferred that the melting temperature of a biodegradable material be substantially lower than its decomposition temperature.